1. Field of the Invention
The present invention relates to a fan device having an ultra thin-type structure with a minimum air gap for reducing an axial thickness. Particularly, the present invention relates to the fan device including a flat-type impeller to provide with an annular supporting plate and a set of bent vanes connected thereto. More particularly, the present invention relates to the flat-type impeller of the fan device to permit the omission of an upraised wall of a hub portion for reducing the entire axial thickness of the fan device.
2. Description of the Related Art
A conventional small-size fan device, as described in U.S. Pat. No. 5,217,351, entitled “SMALL FAN,” includes a fan housing and an impeller rotatably supported therein. The fan housing forms a base plate on which to provide with an axial tube and a pair of stator coils. In common practice, the axial tube accommodates a bearing member which is securely mounted in the axial tube by suitable fastening means. Each of the stator coils has an ordinary or common form of the coil which is circular and flat in form.
Conventionally, provided on the impeller of the fan device are a rotor hub, a set of vane members, a shaft member and a magnet ring member. The rotor hub has an inverted-bowl shape which provides with an outer circumferential surface and an inner space. A series of the vane members are equi-spaced on the outer circumferential surface of the rotor hub, and each of which is extended in a radial direction of the rotor hub. A first distal end of the shaft member is extended into the inner space of the rotor hub, and mounted at a center point of the rotor hub. Correspondingly, a second distal end of the shaft member is extended through and rotatably received in the bearing member.
Generally, the magnet ring member is annular and flat in ordinary form. Mounted in the inner space of the rotor hub is the magnet ring member which is surrounding the shaft member and has a longitudinal alignment with the stator coils. Typically, the magnet ring member provides with at least one or more sets of alternatively opposite magnetic poles corresponding to the number of the stator coils.
In rotational operation, the impeller is turned about the shaft member when the stator coils are actuated to generate an alternatively magnetic field which can repulse the set of the alternatively opposite magnetic poles of the magnet ring member mounted in the impeller. This results in rotation of the impeller to drive cooling air through the fan housing for heat dissipation or ventilation purpose.
In general, a number of design limitations exist for the above-mentioned type of the small-size fan device. These design limitations are given as follows: the fan housing and the impeller of the above-mentioned type of the fan device are typically made of plastic, and are manufactured in a plastic molding process. In order to ensure good molding quality of products and to perfectly cooperate with a molding machine, the rotor hub of the impeller must be sized greater than a predetermined size so that dimensions of the rotor hub cannot be further reduced. In particular, an axial thickness of the rotor hub cannot be further reduced. In addition, in order to combine the rotor hub with the shaft member, the inner space of the rotor hub must provide with an axial seat which is integrally formed and projected from the center point. Inevitably, the axial seat has an axial height that possesses a section of the axial thickness of the rotor hub. Consequently, the axial thickness of the rotor of the conventional small-size fan device cannot be less than 5 mm, for example. Accordingly, there are difficulties in minimizing dimensions and reducing weight of the fan device. Hence, there is a need for improving the design of the conventional small-size fan device to achieve compact and low weight features.
The present invention intends to provide a fan device including a flat-type impeller to provide with an annular supporting plate and a set of bent vanes connected thereto. The annular supporting plate of the flat-type impeller is directly positioned and sandwiched in between an assembling member and a magnet sheet such that the flat-type impeller permits the omission of an upraised wall of a hub portion for reducing the entire axial thickness of the fan device. Accordingly, the flat-type impeller is so configured to carry out a thin-type structure of the fan device in such a way as to mitigate and overcome the above problem.